Hi Rob,
On Mon, Mar 20, 2017 at 6:00 PM, Rob Herring <robh@xxxxxxxxxx> wrote:
> On Mon, Mar 20, 2017 at 10:27 AM, Geert Uytterhoeven
> <geert@xxxxxxxxxxxxxx> wrote:
>> On Mon, Mar 20, 2017 at 4:15 PM, Rob Herring <robh@xxxxxxxxxx> wrote:
>>> On Fri, Mar 10, 2017 at 03:15:20PM +0100, Geert Uytterhoeven wrote:
>>>> Add DT bindings for an Hitachi HD44780 Character LCD Controller where
>>>> its M6800 bus interface is connected to GPIOs.
>>>>
>>>> Memory-mapped configurations are not yet supported.
>>>>
>>>> Signed-off-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
>>
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/auxdisplay/hit,hd44780.txt
>>
>>>> +Required properties:
>>>> + - compatible: Must contain "hit,hd44780",
>>>> + - data-gpios: Must contain an array of either 4 or 8 GPIO specifiers,
>>>> + referring to the GPIO pins connected to the data signal lines DB0-DB7
>>>> + (8-bit mode) or DB4-DB7 (4-bit mode) of the LCD Controller's bus interface,
>>>> + - enable-gpios: Must contain a GPIO specifier, referring to the GPIO pin
>>>> + connected to the "E" (Enable) signal line of the LCD Controller's bus
>>>> + interface,
>>>> + - rs-gpios: Must contain a GPIO specifier, referring to the GPIO pin
>>>> + connected to the "RS" (Register Select) signal line of the LCD Controller's
>>>> + bus interface,
>>>> + - display-height: Height of the display, in character cells,
>>>> + - display-width: Width of the display, in character cells.
>>>
>>> display-{width,height}-chars
>>
>> Makes sense.
>>
>> Greg: As this is already in char-misc-next, shall I send an update for
>> the bindings
>> and the driver?
>>
>>>> +Optional properties:
>>>> + - rw-gpios: Must contain a GPIO specifier, referring to the GPIO pin
>>>> + connected to the "RW" (Read/Write) signal line of the LCD Controller's bus
>>>> + interface,
>>>> + - backlight-gpios: Must contain a GPIO specifier, referring to the GPIO pin
>>>> + used for enabling the LCD's backlight,
>>>
>>> Active state?
>>
>> That's typically handled via the last cell of the GPIO specifier, cfr.
>> GPIO_ACTIVE_HIGH / GPIO_ACTIVE_LOW in <dt-bindings/gpio/gpio.h>.
>
> Yes, I know. I want to be able to read the binding and validate the
> dts file, so I need to know what is the correct flag.
For the LCD Controller's bus, the GPIOs are wired straight, so they should
be ACTIVE_HIGH (unless there's an inverting buffer in between :-).
The backlight is separate from the LCD Controller, hence the polarity
depends on the actual hardware configuration.
Is it worth documenting that?
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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